U.S. patent number 4,655,201 [Application Number 06/630,648] was granted by the patent office on 1987-04-07 for knee orthosis and joint construction therefor.
This patent grant is currently assigned to Northwestern University. Invention is credited to Robert E. Pirmantgen.
United States Patent |
4,655,201 |
Pirmantgen |
April 7, 1987 |
Knee orthosis and joint construction therefor
Abstract
An orthotic joint, and the orthosis with which it is used, for
the protective treatment of ligamentous injuries or deficiencies,
or as a supplement to total joint replacement. The joint includes a
tibial member defining a narrow, upwardly-opening socket and a
femoral member having a planar head portion slidably received
within that socket. Therefore, on each side of the head portion are
a pair of opposing and slidably engaging surfaces, one provided by
the head portion and the other by the side wall of the socket. One
of those opposing surfaces is provided with a recess having its
major dimensions extending in the plane of that surface and having
a narrow cam track about its periphery; the other of the opposing
surfaces being provided with at least one protuberance engageable
with portions of that narrow cam track during flexion and extension
for exerting constraining forces similar to those that would be
exerted by selected ligaments of a patient's knee if such ligaments
were present, healthy, and functioning properly.
Inventors: |
Pirmantgen; Robert E. (Chicago,
IL) |
Assignee: |
Northwestern University
(Evanston, IL)
|
Family
ID: |
24528026 |
Appl.
No.: |
06/630,648 |
Filed: |
July 13, 1984 |
Current U.S.
Class: |
602/16;
623/39 |
Current CPC
Class: |
A61F
5/0123 (20130101); A61F 2005/0165 (20130101) |
Current International
Class: |
A61F
5/01 (20060101); A61F 003/00 () |
Field of
Search: |
;128/8C,8F,8R,88
;3/22,26 ;623/39,43 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
473487 |
|
Mar 1929 |
|
DE2 |
|
826333 |
|
Dec 1951 |
|
DE |
|
1564905 |
|
Apr 1980 |
|
GB |
|
Other References
Orthopaedic Appliances Atlas, pp. 381-382, (The American Academy of
Orthopedic Surgeons, 1952)..
|
Primary Examiner: Crowder; Clifford D.
Attorney, Agent or Firm: Tilton, Fallon, Lungmus
Claims
I claim:
1. An orthotic knee joint assembly comprising a rigid planar
femoral member having a head portion with a narrow arcuate bearing
surface of varying radii of curvature and having a femoral sidebar
projecting from said head portion and adapted to extend upwardly
alongside a wearer's upper leg; a rigid tibial member having a body
portion and a tibial sidebar adapted to extend downwardly alongside
a wearer's lower leg; said body portion having a pair of planar
side walls spaced apart to define a narrow upwardly-opening socket
slidably receiving said head portion and having an arcuate guide
surface engagable with said bearing surface for guiding movement of
said members between flexion and extension along constantly
changing instantaneous axes of rotation; said bearing surface being
slidable posteriorly and anteriorly along said guide surface when
said members are in flexion; and means provided by said members to
direct said bearing surface with respect to said guide surface
during articulation of a patient's knee; wherein the improvement
comprises
said head portion having planar surfaces on opposite sides thereof
slidably engaging said side walls of said body portion within said
socket, whereby, on each side of said head portion are presented a
pair of opposing and slidably engaging surfaces, one provided by
said head portion and the other by said body portion; one of said
opposing surfaces of one of said pairs being provided with a recess
having its major dimensions extending in the plane of such surface
and having a narrow cam track about the periphery thereof; and the
other of said opposing surfaces being provided with a plurality of
protuberances engagable with portions of said cam track during
flexion and extension for exerting constraining forces similar to
those that would be exerted by certain ligaments of the wearer's
knee if such ligaments were present, healthy, and functioning
properly; said recess being substantially larger than said
protuberances so that at any given stage of articulation the
contact between a protuberance and said cam track constrains
movement of said head portion in only certain selected directions
along a plane parallel with said side walls without constraining
movement of said head portion in directions along said plane
opposite from said selected directions; said protuberances being
positioned and arranged for successively engaging portions of said
cam track of said recess during flexion and extension with only one
of said protuberances engaging said track at any given stage of
articulation.
2. An orthotic knee joint assembly comprising a rigid planar
femoral member having a head portion with a narrow arcuate bearing
surface of varying radii of curvature and having a femoral sidebar
projecting from said head portion and adapted to extend upwardly
alongside a wearer's upper leg; a rigid tibial member having a body
portion and a tibial sidebar adapted to extend downwardly alongside
a wearer's lower leg; said body portion having a pair of planar
side walls spaced apart to define a narrow upwardly-opening socket
slidably receiving said head portion and having an arcuate guide
surface engagable with said bearing surface for guiding movement of
said members between flexion and extension along constantly
changing instantaneous axes of rotation; said bearing surface being
slidable posteriorly and anteriorly along said guide surface when
said members are in flexion; and means provided by said members to
direct said bearing surface with respect to said guide surface
during articulation of a patient's knee; wherein the improvement
comprises
said head portion having planar surfaces on opposite sides thereof
slidably engaging said side walls of said body portion within said
socket, whereby, on each side of said head portion are presented a
pair of opposing and slidably engaging surfaces, one provided by
said head portion and the other by said body portion; one of said
opposing surfaces of one of said pairs being provided with a recess
having its major dimensions extending in the plane of such surface
and having a narrow cam track about the periphery thereof; and the
other of said opposing surfaces being provided with at least one
protuberance engagable with portions of said cam track during
flexion and extension for exerting straining forces similar to
those that would be exerted by certain ligaments of the wearer's
knee if such ligaments were present, healthy, and functioning
properly; said recess being substantially larger than said
protuberance so that at any given stage of articulation the contact
between said protuberance and said cam track constrains movement of
said head portion in only certain selected directions along a plane
parallel with said side walls without constraining movement of said
head portion in directions along said plane opposite from said
selected directions; one of said opposing surfaces of the other of
said pairs being provided with a second recess having its major
dimension extending in the plane of such surface and having a
second narrow cam track about the periphery thereof; and the other
of said opposing surfaces of said other pair being provided with at
least one second protuberance engagable with portions of said
second cam track during flexion and extension for exerting
constraining forces similar to those that would be exerted by
selected ligaments of the wearer's knee if such ligaments were
present, healthy, and functioning properly; said second recess
being substantially larger than said second protuberance so that at
any given stage of articulation the contact between said second
protuberance and said second cam track contrains movement of said
head portion in only certain selected directions along a plane
parallel with said side walls without constraining movement of said
head portion in directions along said plane opposite from said
selected directions; said first and second protuberances being
positioned and arranged for successively engaging their respective
cam tracks so that only one of said protuberances is engagable with
its cam track at any given intermediate stage of articulation
between full extension and flexion.
3. The assembly of claim 2, in which stop means are provided along
the anterior of said femoral sidebar adjacent said head portion;
said stop means being engagable with the anterior of said body
portion for limiting the degree of maximum extension of said joint
assembly.
4. The assembly of claim 3 in which said stop means is adjustable
along said femoral sidebar for engaging and stopping said body
portion at any of a multiplicity of angular positions of said
tibial member relative to said femoral member and thereby
selectively varying the angular degree of maximum extension of said
joint assembly.
5. The assembly of claim 4 in which said stop means comprises a
member of U-shaped cross section engaging the lateral, medial, and
anterior surfaces of said femoral sidebar; and locking means for
anchoring said U-shaped member in selected positions of adjustment
along said femoral sidebar.
6. The assembly of claim 3 in which said assembly is a component of
a complete knee orthosis; said orthosis including a second assembly
similar to said first-mentioned assembly; means for securing said
femoral sidebars along opposite sides of a patient's upper leg; and
means for securing the tibial sidebars along opposite sides of a
patient's lower leg.
7. The assembly of claim 2, in which said assembly is a component
of a complete knee orthosis; said orthosis including a second
assembly similar to said first-mentioned assembly; means for
securing said femoral sidebars along opposite sides of a patient's
upper leg; and means for securing the tibial sidebars along
opposite sides of a patient's lower leg.
Description
BACKGROUND
U.S. Pat. No. 4,361,142 discloses a knee orthosis having a pair of
knee joint assemblies 13 and 14 positioned on opposite sides of a
patient's knee, each assembly having a femoral sidebar 15 and a
tibial sidebar 16 extending alongside the upper and lower leg,
respectively. The upper femoral sidebars are held along the upper
leg by suspension means in the form of interfacial member 17,
straps 20, 21, and pad 26 and, similarly, the lower tibial sidebars
are immobilized along opposite sides of the lower leg by suspension
elements in the form of interfacial members 18 and 19 and straps
22-24.
At the upper end of each tibial sidebar is a body portion 40 having
a pair of planar side walls spaced apart to define a narrow
upwardly-opening socket 38 that slidably receives the head portion
34 of a femoral member 30 of which the upper femoral sidebar 15 is
an integral part (FIG. 2). Within the socket is a narrow arcuate
guide surface 39 that engages the bearing surface 35 of the femoral
member for guiding movement of the members between flexion and
extension along constantly changing instantaneous axes of rotation.
When the joint is in flexion as shown in FIG. 8, the head 34 would
be capable of limited sliding movement posteriorly and anteriorly
along the guide surface 39 in the absence of some additional
constraining force. The interfitting relationship therefore assures
stability at all degrees of flexion but there is nevertheless
sufficient laxity in the mechanical joint to permit normal action
of the patient's knee. Healthy ligaments are allowed to control
natural knee movement. At the same time, at least one flexible but
non-stretchable strap 33, and ordinarily a plurality of such straps
(three are shown in FIG. 2), secured at selected points to the
respective members of the orthotic joint, perform essential
functions that would normally be performed by the injured or
chronically deficient ligament, thereby protecting that ligament
without interfering with the functions of the healthy ligaments.
The positions and connections of the straps depend on the ligament
or ligaments requiring protection or the stability required if such
ligament or ligaments are absent. In any case, for any grouping of
straps there is a sequential tensioning and untensioning of such
straps during flexion and extension, with the result that the
injured or deficient ligament is protected at all degrees of
flexion.
The arrangement and positioning of straps 33 depend on the
particular ligament or ligaments requiring protection. FIGS. 1-8
illustrate the attachment and positioning of straps for a patient
with injury to or chronic deficiency of the posterior cruciate
ligament. A primary function of that ligament in a normal knee
joint is to pull the head of the femur in a posterior or rearward
direction over the tibial articular surface during flexion and to
hold it in a rearward position when the knee is fully flexed. The
articulation of the femoral member 30 and tibial member 31 of the
orthotic joint mimics the articulation of the natural joint, and
the set of straps 33 is mounted to exert forces during flexion, as
well as at extension and 90.degree. flexion, that mimic forces that
would normally be exerted by a natural posterior cruciate ligament.
For a patient whose condition requires protection of other major
ligaments, the straps and their points of attachment would be
different. For example, FIG. 9 depicts an orthotic joint for use
with a patient having an injured or chronically deficient anterior
cruciate ligament, and FIG. 10 illustrates a joint with strap
attachment points arranged for protection of a collateral
ligament.
While the orthosis briefly described above and disclosed in detail
in U.S. Pat. No. 4,361,142 is considered superior to previous
orthoses because, among other things, there is sufficient laxity in
the mechanical joint to permit healthy ligaments to control natural
knee movement, proper operation of the orthotic joint in protecting
the injured or deficient ligaments requires precise adjustment of
the length and location of attachment of the straps 33. Slight
stretching of the straps over a period of extended use reduces the
protective function of the orthosis. While problems of stretching
might be reduced by forming the straps or cables of metal (as
indicated in the patent), the constant flexing and tensioning of
those straps or cables may nevertheless produce dimensional changes
that require periodic inspection and possible adjustment or
replacement. Wear on those straps or cables, and their points of
connection is inevitable, especially in view of the exposed
condition of those elements. Also, because the straps are exposed
and bulge outwardly when they are untensioned, such straps are
vulnerable to contact with objects or clothing that might interfere
with their proper operation.
SUMMARY OF THE INVENTION
This invention is therefore concerned with a knee orthosis, and the
joint construction for such an orthosis, which achieves the
advantages of the structure disclosed in U.S. Pat. No. 4,361,142
without the disadvantages described above. Specifically, this
invention is directed to an orthotic joint (and the orthosis with
which it is used) which provides sufficient laxity so that it does
not constrain normal movements of a patient's knee but nevertheless
is capable of restraining abnormal knee movements (or, in the case
of prosthetic joint replacement, preventing movements that do not
conform with the prescribed action of the replacement joint)
without the use of external flexible straps or cables.
As in the patented construction, the joint assembly includes a
rigid planar femoral member having a head portion with a narrow
arcuate bearing surface of varying radii of curvature and having a
femoral sidebar projecting from that head portion and adapted to
extend upwardly alongside a wearer's upper leg. The assembly also
includes a rigid tibial member having a body portion and a tibial
sidebar adapted to extend downwardly alongside a wearer's lower
leg. The body portion has a pair of planar side walls spaced apart
to define a narrow upwardly-opening socket that slidably receives
the head portion of the femoral member. The socket includes an
arcuate guide surface that is engagable with the bearing surface of
the femoral member for guiding movement of the two members between
flexion and extension along constantly changing instantaneous axes
of rotation.
In the joint assembly of this invention, the head portion has
planar surfaces on its opposite sides that slidably engage the side
walls of the body portion within the socket; therefore, on each
side of the head portion there are presented a pair of opposing and
slidably engaging surfaces, one provided by the head portion and
the other by the body portion. One of those surfaces of each pair
is provided with a recess that has its major dimensions extending
along the plane of such surface and having a narrow cam surface or
track extending about the periphery of the recess. The outer of the
opposing surfaces of each pair is provided with at least one
protuberance engagable with portions of the narrow cam track of the
opposing surface during at least a portion of the full range of
travel between flexion and extension for exerting constraining
forces similar to those that would be exerted by certain ligaments
of the wearer's knee if such ligaments were healthy and functioning
properly. The protuberances, cam tracks, and recesses are
dimensioned and shaped to permit a laxity or play in the orthotic
joint that allows the healthy ligaments of the knee, those that are
not being protected by the orthosis, to function in their normal
manner without interference by the orthosis.
The orthosis also includes adjustable stop means for limiting the
degree of extension of the orthotic joint and, hence, the degree of
extension of the wearer's leg. Adjustment of the stop not only
permit the orthosis to be adjusted to meet the specific needs of a
patient but also allows progressive re-setting of the stop as
healing occurs following injury or surgery.
Other features, advantages, and objects will become apparent from
the specification and drawings.
DRAWINGS
FIG. 1 is a perspective view of a knee orthosis embodying the
present invention.
FIG. 2 is a perspective view of one of the orthotic joints of that
orthosis.
FIG. 3 is an exploded perspective view of an orthotic joint of the
type shown in FIG. 2 with the components of such joint constructed
for treatment of a patient with injury to or deficiency of the
collateral ligaments.
FIGS. 4A and 4B are schematic elevational views of opposite sides
of the joint of FIG. 3 with the members thereof in full
extension.
FIGS. 5A and 5B are similar to FIGS. 4A and 4B but depict the
femoral member at approximaly 45.degree. flexion.
FIGS. 6A and 6B show the femoral member at approximately 90.degree.
flexion.
FIGS. 7A and 7B show the femoral member at maximum flexion.
FIG. 8 is an exploded perspective view of an orthotic joint
embodying the invention and constructed for treatment of injury to
or deficiency of the posterior cruciate ligament.
FIGS. 9A and 9B are schematic or diagramatic elevational views
showing the joint of FIG. 8, viewed from opposite sides, in full
extension.
FIGS. 10A and 10B show the same joint at 45.degree. flexion.
FIGS. 11A and 11B at 90.degree. flexion.
FIGS. 12A and 12B at maximum flexion.
FIG. 13 is an exploded perspective view of an orthotic joint
constructed for treating injury to or deficiency of the anterior
cruciate ligament.
FIGS. 14A and 14B are schematic elevational views of opposite sides
of the joint of FIG. 13 showing the members at approximately
90.degree. flexion.
FIGS. 15A and 15B illustrate the same joint at approximately
45.degree. flexion.
FIGS. 16A and 16B depict the members at full extension.
DETAILED DESCRIPTION
Referring to FIG. 1, the numeral 10 generally designates a knee
orthosis embodying the invention, the orthosis being shown as it
might be worn on the left leg 11 of a patient. The orthosis
consists essentially of a pair of knee joint assemblies 13 and 14
positioned on opposite sides of the patient's knee 11a, each
assembly having sidebars 15 and 16 extending alonside the upper leg
11b and lower 11c, respectively, and means for holding the
assemblies in such positions. In the embodiment illustrated, such
means takes the form of rigid or semi-rigid interfacial members or
plates 17, 18, and 19, and suspension members or straps 20, 21, 22,
23, and 24. The upper or proximal plate 17 is shaped to conform to
the contour of the anterior upper leg 11b and is securely connected
to the upper ends of femoral sidebars 15 by means of rivets 17a or
any other suitable connecting means. The suspension strap 20 is
permanently joined at one end to one of the sidebars (or to one end
of plate 17) and is detachably connected at its other end to the
other sidebar or to the outer surface of plate 17 adjacent to the
other sidebar. Such releasable attachment may be achieved by
securing Velcro patches 17b to the overlapping portions of strap 20
and interfacial member or plate 17.
Suspension strap 21 is similarly secured to the femoral sidebars 15
of the orthosis. One of the sidebars may be equipped with an
extension plate 25 that may, if desired, be enlarged to extend
across the anterior upper leg 11b to the other femoral sidebar, and
a resilient medial pad or cushion 26 may be secured to the opposite
sidebar for the purpose of achieving proper positioning and fit of
the orthosis and to increase wearer comfort. The suspension strap
21 works in conjunction with cushion 26 and extension plate 25 to
help immobilize the femoral sidebars 15 of the orthosis with
respect to the femur, thereby complementing interfacial member 17
and suspension strap 20. In that connection, reference may be had
to co-pending co-owned application Ser. No. 630,649, filed July 13,
1984, now U.S. Pat. No. 4,565,190 for the details of what are
believed to be improvements in femoral suspension construction.
The lower or distal interfacial member or plate 18 is shaped to
conform to the contour of the anterior lower leg and is similarly
secured to the distal ends of tibial sidebars 16 by rivets 18a.
Such rivets also permanently join one end of the suspension strap
22 to one of the sidebars 16, and Velcro patches 18b releasably
join the opposite end of the strap to rigid member 18. The purpose
of the interfacial members and straps is to immobilize the femoral
and tibial sidebars in relation to the upper and lower leg of the
wearer, and to maintain the orthotic joints in proper alignment
with the wearer's knee. To achieve those objectives, various
modifications or alterations may be made in the suspension system
and different means for immobilizing the sidebars and for locating
the joint assemblies might be provided. For example, the sidebars
15 and 16 might be embedded in plaster casts formed about the
wearer's leg above and below the knee, as in the case where
near-anatomical joint motion is needed to prevent knee damage while
a patient recovers from a femoral fracture. Since the present
invention is not concerned with the construction of the suspension
system or with any specific means for achieving immobilization of
the femoral and tibial sidebars and the joint assemblies of the
orthosis, further detailed description of such suspension means is
believed unnecessary herein.
The joint assemblies 13 and 14 on opposite sides of the wearer's
leg are basically the same in construction, the main differences
being that they are reverse or mirror images of each other with the
sidebars 15 and 16 of somewhat different length and configuration
to follow the differences in contour of the wearer's leg. There may
also be differences in the recess and protuberance construction (as
described hereinafter) between the hinge assemblies on opposite
sides of the knee depending on the particular ligamentous injury
being treated although, in general such arrangements would
ordinarily be the same. While the details of the left assembly 13
are shown in the drawings, and are described hereinafter, such
detailed disclosure should be understood as also being applicable
to the right assembly 14.
Each orthotic joint assembly includes two basic components: a
femoral member 30 and a tibial member 31. The femoral member 30 is
planar and includes, as an integral portion thereof, the upstanding
elongated femoral sidebar 15. In addition, the femoral member has
at its lower end an enlarged planar head portion 34. The head
portion has an arcuate bearing surface 35 of varying radii of
curvature with the posterior portion 35a of that surface having
smaller radii of curvature than the distal portion 35b thereof. In
general, the curvature of bearing surface 35 simulates or conforms
to the curvature of a femoral condyle viewed in sagittal section.
It will be noted, however, that the leading or anterior portion 35c
of the bearing surface is substantially straight and constitutes an
extension of the leading edge of femoral sidebar 15. While the
femoral member 30 may be formed of any strong, rigid, and durable
material, it is believed that a lightweight metal such as aluminum
is particularly effective.
The head portion 34 of the femoral member is received with an
upwardly-facing socket 36 provided by body portion 37 of tibial
member 31. The tibial member includes both the socket-providing
body portion 37 and the depending tibial sidebar 16. The two
portions may be formed integrally of the same rigid material
although it is believed preferable to fabricate body portion 37
from a rigid polymeric material such as polypropylene or a
polypropylene-polyethylene copolymer (90/10% formulation has been
found effective) and to embed the upper end of the tibial sidebar
16, formed of aluminum or other material having similar properties,
within the body portion as indicated. The body portion 37 is shown
to be formed in two sections, namely, a lateral section 37a and a
medial section 37b. Ideally, socket 36 is formed by molding,
casting, or machining the two sections so that the lateral section
37a of the body portion defines one half 36a of socket 36, and the
other section 37b defines the other half 36b of the socket (FIG.
3); however, if desired, the socket may be molded or otherwise
formed entirely in one of the sections. In any event, the body
portion 37 includes a pair of opposing, parallel, planar side wall
surfaces 38 that, together with a narrow arcuate guide surface 39
(provided jointly by the two sections 37a and 37b), define socket
36. The guide surface 39, when viewed in outline, corresponds
closely to the curvature of bearing surface 35 of femoral member
30. Maximum contact between such surfaces occurs when the members
are in extension (FIGS. 4A and 4B). In that condition of close
conformity, with the substantially straight leading surface 35c of
the femoral head portion abutting the substantially straight
anterior portion of the guide surface 39, the femoral and tibial
members are restrained against both hyperextension and
posterior-anterior sliding translation. Because the curvature of
the posterior portion 35a of the arcuate femoral bearing surface 35
is of smaller radii than the distal portion 35b thereof, the extent
of contact between bearing surface 35 and guide surface 39
decreases during flexion (FIGS. 5A, 5B, 6A, 6B, 7A, 7B). As the
degree of flexion increases, the more limited contact between the
bearing and guiding surfaces, and the decreased anterior-posterior
dimension of the head portion 34 in relation to that of socket 36,
allows limited anterior-posterior sliding movement of the head
portion within the socket, at least in the absence of some natural
or artificial constraining means. Thus, referring to FIGS. 5A
through 7B, in the absence of some constraining means, head portion
34 would be free to slide anteriorly a limited distance within
socket 36 until its curved distal surface engages the straight
anterior surface of the socket.
The sections 37a and 37b of the body portion 37 are fused or
otherwise permanently joined together in the finished product. The
spacing between the opposing faces 36a and 36b of the socket is the
same as, or only slightly greater than the distance between the
lateral and medial planar surfaces 34a and 34b of head portion 34
of the femoral member. Therefore, when the parts are assembled, a
coplanar relationship is maintained with the planar surfaces on
opposite sides of the head portion 34 being in sliding engagement
with the planar surfaces 38 within the socket. Stated differently,
in the assembled joint there are a pair of opposing and
slidably-engagable surfaces along each side of the head portion,
one pair constituting lateral surface 34a of the head portion and
inner surface 38 of section 37a of the body portion, and the other
pair comprising medial surface 34b of the head portion and surface
38 of the medial section 37b of the body portion 37.
An arcuate or crescent-shaped recess 40 is formed in
socket-defining surface 38 of the lateral section 37a of the tibial
body portion 37. The shape of the recess is developed to perform a
camming function, and a narrow cam surface or track 40a defines the
periphery of that recess. It will be observed that the major
dimensions of the recess extend in a plane parallel with surface
38. Recess 40 receives protuberances 41 and 42 projecting laterally
from the head portion of femoral member 30. Two such protuberances
are shown for clarity of illustration and ease of manufacture, but
it should be understood that such protuberances may be merged
together to form a single protuberance having portions capable of
making sequential contact with cam track 40a during flexion and
extension in the manner hereinafter described.
A similar recess 43, but of different shape, is formed in the
surface 38 of the medial section 37b of the body portion 37. Like
recess 40, recess 43 has its greatest dimensions extending in the
plane of surface 38 and has its periphery defined by a narrow
bearing surface or track 43a. That track is engagable with one or
more medial protuberances 44 projecting medially from surface 34b
of the head portion 34 of the femoral member.
An adjustable stop member 50 is mounted upon femoral member 30 just
proximal to head portion 34. The stop member is generally U-shaped
when viewed in horizontal section and has side portions 50a that
engage the lateral and medial surfaces of the femoral sidebar 15
just proximal to head portion 34. Screws or bolts 51 extend through
slots 52 and openings 53 and may be tightened to clamp the side
walls 50a into tight locking engagement with the lateral and medial
surfaces of sidebar 15.
The operation of the joint assembly is somewhat schematically
depicted in FIGS. 4A through 7B with figures bearing the same
numerals but different letters showing the assembly from opposite
sides under the same condition of flexion. Thus, FIGS. 4A and 4B
illustrate the assembly from opposite sides under a condition of
full extension, and FIGS. 7A and 7B show the same assembly under a
condition of maximum flexion. Only the recesses and protuberances
facing the viewer are shown in each view with the protuberance that
is operative at each of the illustrated degrees of flexion being
fully shaded and the non-operative protuberance(s) being depicted
in solid lines (for clarity of illustration) but unshaded.
The orthotic joint assembly of FIGS. 3 through 7B is intended for
use by a patient having injury to or deficiency of the collateral
ligaments. In a normal knee joint, the collateral ligaments
function primarily to prevent vertical separation (i.e.,
proximal-distal separation or superior-inferior separation) between
the femoral and tibial components, and they do so without at the
same time preventing limited anterior-posterior displacement of
such components as the leg is flexed. Anterior-posterior travel of
the head of the femur in relation to the condyles of the tibia is
controlled largely by the anterior and posterior cruciate
ligaments. The orthotic joint of FIGS. 3-7B protects abnormal
operation of the knee joint that might result from a deficiency of
the patient's collateral ligaments caused by injury, surgery, or
other possible reasons, without interfering with normal operation
of the patient's healthy cruciate ligaments. Natural action of the
knee joint is therefore permitted, the function of the orthosis
being to reinforce or protect the knee against abnormal operation
because of the deficient (or possibly absent) collateral
ligaments.
In a condition for full extension, the head portion 34 of the
femoral member 30 is seated within socket 36 with its bearing
surfaces fully engaging the corresponding guide surfaces defining
that socket. Vertical separation between the elements of the
orthotic joint is prevented because of engagement between
protuberance 41 and (an upper portion of the cam track) at the
extreme right end of recess 40 as viewed in FIG. 4A. Protuberance
41 is shaded in that figure to indicate that of the three
protuberances 41, 42, and 44, it is the only one that functions at
that moment to prevent such separation. It will be observed in
FIGS. 4A and 4B that protuberances 42 and 44 do not engage portions
of the cam tracks of the recesses in which they are disposed;
therefore, if it were not for protuberance 41, the femoral member
30 could be shifted upwardly a limited extent with respect to
tibial member 31.
In a condition of partial flexure of the orthotic joint,
specifically, with the femoral member at an angle of about
45.degree. from the vertical, protuberance 41 remains in engagement
with the upper cam track of recess 40 and continues to prevent
relative upward displacement of the femoral member 30. However,
neither it nor the other protuberances 42, 44 prevent limited
anterior-posterior movement of the femoral member 30 in relation to
socket 36. Such movement of the femoral member is also possible at
90.degree. flexion (FIGS. 6A, 6B) as indicated by arrow 61, and
even when the joint is fully flexed as represented by arrow 62
(FIGS. 7A, 7B). However, when the joint is at about 90.degree.
flexion, protuberance 44 and the upper cam track of recess 43
become operative to prevent vertical movement of the femoral head
34 within its socket 36. The narrow upper cam track of recess 43
serves to guide the head should anterior-posterior forces be
exerted in the direction of arrow 61. When the joint is fully
flexed (FIGS. 7A, 7B), protuberance 44 and the upper cam track of
recess 43 remain operative, and protuberance 42 and the cam track
of recess 40 become operative, to prevent relative superior
movement of the femoral head without at the same time preventing
limited anterior-posterior movement.
Since the orthotic joint does not prevent limited relatively
anterior-posterior movement of the femoral head within its socket
when the joint is in any stage of partial to complete flexure
(FIGS. 5A through 7B), and since such movement of the natural joint
is controlled by the cruciate ligaments, the patient's cruciate
ligaments are allowed to function normally without being
constrained by the orthotic joint. The orthotic joint of FIGS. 3-7B
mimics only those forces that would normally be exerted by normal,
healthy collateral ligaments. Therefore, the orthosis may be worn
to provide temporary protection for the deficient collateral
ligaments as they heal from injury or surgery, or as a more
permanent back-up for collateral ligaments that are irreparably
damaged or deficient, or even as a functional substitution in a
case where the patient's collateral ligaments are totally
inoperative.
Referring to FIGS. 4A and 4B, it will be observed that the leading
lower edge of stop 50 engages the upper surface of tibial member 31
when the joint is fully extended. Under such circumstances, the
stop 50 simply functions as a reinforcement against possible
hyperextension, performing the same function previously described
in connection with protuberance 41 and recess 40. However, in some
instances even full extension as shown in these figures is to be
avoided during a period of treatment or recovery, in which case an
orthopedic specialist may shift stop 50 downwardly sightly and lock
it in its adjusted position by screws 51, so that the lower end of
the stop will engage the tibial member 31 just before full
extension occurs. The distance which stop 50 is lowered depends, of
course, upon the patient's condition and the treatment required
and, subject to those considerations, periodic readjustment of the
stop in an upward direction may be deemed desirable over the term
of recovery. Thus, injured ligaments may be allowed to assume a
progressively greater role in preventing hyperextension as the
healing process continues.
FIGS. 8-12B show a joint assembly 13' that is identical to the
assembly of FIGS. 3-7B except for differences in the recesses,
their cam surfaces or tracks, and the protuberances which engage
those tracks. The orthotic joint of FIG. 8 is intended for a
patient with a damaged or deficient posterior cruciate ligament,
the other knee ligaments being operative and not requiring
protective treatment. A primary function of the posterior cruciate
ligament is to draw the femur in a posterior direction during
flexion and to restrain it in a posterior location when the knee is
so flexed. The orthotic joint 13' mimics the function of a normal
posterior cruciate ligament in that respect without assuming
functions performed by other ligaments such as, for example, the
collateral ligaments. Thus, it will be evident from FIGS. 10A, 10B,
11A, and 11B that slight upward movement of femoral member 30 with
respect to tibial member 31 will be possible without any
restraining action by the orthotic joint, the extent of such
movement being indicated in these figures by phantom lines. Such
relative upward movement of the femur in the natural joint is
prevented by collateral ligaments and, since it is assumed that the
patient's collateral ligaments are healthy and operative, the
orthotic joint 13' does not interfere with the normal action of
those collateral ligaments.
The sizes, positions, and shapes of recesses 40' and 43' differ
from those of recesses 40 and 43. Also, there are only two
protuberances 42', 44' rather than three, and their locations
differ from those of protuberances 42, 44. When the leg is fully
extended, protuberance 42' and the peripheral cam track of recess
40' are not operative (while protuberance 42 is shown in FIG. 9A in
contact with the lower track of recess 40', the head portion of
femur 34 is already fully seated within its socket); however, the
peripheral cam track of recess 43' cooperates with protuberance 44'
to prevent relative upward displacement of the femoral head portion
34 with respect to tibial member 31. As the femoral member 30
swings into a flexed condition (FIGS. 10A-11B), protuberance 42'
rides forwardly (anteriorly) and upwardly (proximally) along the
arcuate lower cam track of recess 40' to urge the femoral head
portion 34 rearwardly (posteriorly). During such flexion,
protuberance 44' and the cam track of recess 43' are generally
inoperative; however, in a state of maximum flexion, both of the
protuberances 42', 44' engage the cam tracks of their respective
recesses 40', 43' to prevent upward movement of the femoral head
portion 34 within socket 36.
FIGS. 13-16B show an orthotic joint 13" which is the same as
previously-disclosed joints 13 and 13' except for further
variations in the sizes, shapes, and locations of the recesses 40',
43" and the number and positions of protuberances 41", 42", and
44". Joint assembly 13" would be used in an orthosis for a patient
having an injured or deficient anterior cruciate ligament. That
ligament normally urges the head of the femur of the knee joint
forwardly (anteriorly) as the leg is extended. Therefore, as the
orthotic joint shifts between a position of 90.degree. flexion, to
45.degree. flexion, and then to extension, the cam surfaces of the
recesses and the protuberances that serve as cam riders urge the
head portion 34 in an anterior direction without at the same time
constraining or interfering with the action of the patient's knee
joint ligaments except for the anterior cruciate ligament.
At 90.degree., protuberance 42" engages the cam track of recess 43"
to limit rearward (posterior) displacement of the head of femoral
member 30 within its socket 36 (FIG. 14B). As extension continues,
protuberance 44" becomes operative to direct the femoral head
portion forwardly (anteriorly) (FIG. 15B) and, finally, when full
extension is achieved, protuberance 41" coacts with the peripheral
cam track of recess 40" to hold the head portion in its forward
(anterior) position (FIG. 16A).
In each construction, the protuberances function as cam riders and
coact with the narrow cam surfaces or tracks of the recesses to
prevent abnormal movements of the knee where the ligament group
that normally functions to prevent such abnormal movements is
lacking or deficient. At the same time, the orthotic joint does not
interfere with the functioning of normal or healthy ligaments of
the patient's knee. To achieve such stability while at the same
time providing the desired laxity in the operation of the joint,
more than one area of cam action is believed necessary. Where there
is more than a single protuberance along one side of the femoral
head portion, those protuberances might of course be joined into a
single protuberance having plural zones of sequential contact with
the associated cam surface or track. While it is believed important
to have two cam-providing recesses to achieve the multiple
functions required, it is also believed apparent that the
arrangement of cam recesses and protuberances or projections might
be reversed, so that what is shown on the medial side of the
femoral head portion might be located on the lateral side, and vice
versa, and further, that the projections or protuberances might
instead be provided by the walls of the socket with such
protuberances then extending into cam-defining recesses formed in
opposite sides of the femoral head portion.
While in the foregoing, embodiments of the invention have been
disclosed in considerable detail for purposes of illustration, it
will be understood by those skilled in the art that such details
may be varied without departing from the spirit and scope of the
invention.
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